Conveyor belts sometimes include fixed, stacked rollers that are used to propel objects rearward along the conveyor belt as it advances. The roller at the bottom of the stack rolls on a bearing surface underlying the conveyor belt as the conveyor belt advances along a conveyor. The forward rotation of the rolling bottom roller contacting the top roller in the stack causes the top roller to rotate in the opposite direction to propel objects conveyed atop the rollers to be pushed rearward on the conveyor belt. As the top and bottom rollers wear, contact between the bottom rollers and the top rollers deteriorates.